The present invention relates generally to radio communications systems, and more particularly to an improved method and apparatus for communicating variable length messages between a primary station and remote stations of a data communications system.
In prior art data communications sytems, as exemplified by the system described in U.S. Pat. No. 4,156,867, messages communicated from a central station to mobile stations included a start code followed by one or more data blocks each including a parity word and a number of digital words with a data and parity portions. No information is provided in the first or second block as to the number of following blocks, and no provision was made for efficiently and reliably accomodating long strings of data. The bits of the data block were interleaved so as to be more tolerant of burst errors. However, the interleaving scheme of these prior art data communications systems typically rendered blocks susceptible to the loss of either a group of data bits or a group of parity bits due to burst errors. Furthermore, simultaneous transmissions from two or more mobile stations could interfere with one another such that neither was adequately received by the central station.